Method for locating a badge for a motor vehicle hands-free system

ABSTRACT

This process comprises the following steps:  
     transmission in the form of an enquiry ( 14 ) of a signal by a first group of antennas of the vehicle to the tag,  
     possible response ( 16 ) of the tag to this first enquiry,  
     transmission in the form of an enquiry of a signal ( 18 ) by a second group of antennas of the vehicle to the tag,  
     possible response ( 20 ) of the tag to this second enquiry.  
     In case of response ( 16 ) of the tag to the first enquiry ( 14 ), the tag stores for a predetermined time span the fact that it has responded to a signal transmitted by an antenna of the first group of antennas. The possible response ( 20 ) made to the second enquiry ( 18 ) includes, as the case may be, a cue indicating that a response has already been transmitted following an enquiry originating from the first group of antennas.

[0001] The present invention relates to a process for locating a tagused in particular for a hands-free system of a motor vehicle.

[0002] A hands-free system makes it possible to access one's vehicle andto start the latter without having to use a mechanical key. The user ofthe vehicle is then simply furnished with an electronic card (alsoreferred to hereinafter as a tag) which is detected and recognized by acontrol and management device associated with antennas disposed on boardthe vehicle. If the card is identified by the control and managementdevice as being a card authorized for the vehicle, the carrier of thiscard can enter inside the vehicle by simply grasping a door handle andstart the engine of the vehicle by simple action on a button.

[0003] It will be noted that the term “tag” in fact covers any keysystem whether or not it comprises a rigid electronic card (example:electronic components placed on a flexible circuit, or on a hybridcircuit, etc).

[0004] Generally, for such a hands-free system, a group of antennas isintended to detect the presence of the tag outside the vehicle andanother inside the latter. If an authorized tag is detected outside thevehicle, the control and management system will allow access on boardthe vehicle without however allowing starting, whereas if this tag isinside the vehicle, starting of the engine will be able to occur.

[0005] To locate the tag, a signal is sent to a group of antennas whichthen carry out a corresponding transmission while no signal is sent tothe other antennas so that they remain mute. The antennas used are LF(low frequency) antennas transmitting a magnetic field with a frequencyusually lying around 125 kHz with a restricted range thus allowing goodlocating of the corresponding tag. The dialogs between the insideantennas and the tag are of a different kind from the dialogs betweenthe outside antennas and tag. This enables the tag to know in advancethe response expected by the vehicle. This response is generallyeffected by transmitting an RF (radio frequency) signal with a frequencygenerally lying in the vicinity of 433 MHz.

[0006] The inside antennas are generally regarded as reliable. The fieldtransmitted by them does not generally spill over out of the cabin ofthe vehicle. On the other hand, the outside antennas generally transmita signal inside the cabin of the vehicle too, generally limited to nearthe latter's doors. A tag is then regarded as being outside the vehicleif it responds to the outside antennas without however responding to theinside antennas.

[0007] The locating of a tag outside the vehicle is therefore based on anonresponse of the tag to a request by the inside antennas. It mayhowever happen that the tag responds to a request by the inside antennasbut that this response is not received by the antennas managementdevice. This problem may stem from several causes, such as for examplethe presence of glitches or the sending of an RF frame of another systemusing the same frequency band. This nonreceipt of the response by thevehicle antennas management system will be interpreted as a nonresponseto the request of the inside antennas and the tag will then be regardedas being outside the vehicle although it is in fact inside the latter.The management device will therefore give its agreement to execute anorder to lock the vehicle although the user does not have his tag onhim. Moreover, anybody will be able to unlock the vehicle with the tagstill in the vehicle.

[0008] An aim of the present invention is thus to provide a process forlocating a tag intended for a motor vehicle hands-free system allowingreliable detection of the presence of a tag outside the vehicle.

[0009] Accordingly, the process that it proposes is a process forlocating a tag for a hands-free system of a motor vehicle comprising thefollowing steps:

[0010] transmission in the form of an enquiry of a signal by a firstgroup of antennas of the vehicle to the tag,

[0011] possible response of the tag to this first enquiry,

[0012] transmission in the form of an enquiry of a signal by a secondgroup of antennas of the vehicle to the tag,

[0013] possible response of the tag to this second enquiry.

[0014] According to the invention, in case of response of the tag to thefirst enquiry, the tag stores for a predetermined time span the factthat it has responded to a signal transmitted by an antenna of the firstgroup of antennas and the possible response made to the second enquiryincludes, as the case may be, a cue indicating that a response hasalready been transmitted following an enquiry originating from the firstgroup of antennas, the tag then being located in the zone covered by thefirst group of antennas if a response is obtained following the firstenquiry, in the zone covered by the second group of antennas if aresponse is obtained following the second enquiry and in the overlapzone covered by the two groups of antennas if the response to the secondenquiry furthermore contains a complementary indication indicating thatthe tag has already responded earlier.

[0015] In one form of implementation of this process, the first group ofantennas comprises for example antennas transmitting an electromagneticsignal with a range limited substantially to the inside of the vehicle.The second group of antennas comprises for example antennas transmittingan electromagnetic signal with a range limited essentially to theoutside of the vehicle.

[0016] The present invention also proposes a process for locating, for ahands-free system of a motor vehicle, a tag situated outside thevehicle, the vehicle being equipped with inside antennas transmitting anelectromagnetic signal inside the cabin of the vehicle and outsideantennas transmitting an electromagnetic signal essentially outside thecabin with a possible spillover inside the cabin, this processcomprising the following steps:

[0017] transmission in the form of an enquiry of a signal by the insideantennas of the vehicle to the tag,

[0018] possible response of the tag to this first enquiry,

[0019] transmission in the form of an enquiry of a signal by the outsideantennas of the vehicle to the tag,

[0020] response of the tag to this second enquiry.

[0021] In this process, according to the invention, in case of responseof the tag to the first enquiry, the tag stores for a predetermined timespan the fact that it has responded to a signal transmitted by an insideantenna and in that the response made to the second enquiry includes, asthe case may be, a cue indicating that a response has already beentransmitted following an enquiry originating from the inside antennas,the tag then being located outside the vehicle when a response isreceived following the second enquiry and this response comprises noparticular indication.

[0022] Here there are two groups of antennas, the inside antennascorresponding to the first group of antennas and the outside antennas tothe second group of antennas.

[0023] The signals transmitted by the two groups of antennas arepreferably low-frequency signals of the order of 125 kHz. Signals ofthis type are already conventionally used since they allow in particularbetter control of the zone of coverage of the antennas. The response ofthe tag is preferably made in a radio frequency of the order of 433 MHz.

[0024] For proper sequencing of the various steps of the process, it ispreferable for the enquiry performed by the second group of antennas tobe carried out long enough after the enquiry performed by the firstgroup of antennas to allow the tag time to respond to an enquiry beforeit receives another one.

[0025] All the antennas of one and the same group of antennas maysimultaneously transmit their enquiry signal for the locating of the tagbut, to limit the power of the signal transmitted, the antennas of oneand the same group of antennas may also transmit one after another anenquiry to the tag.

[0026] The details and advantages of the present invention will emergebetter from the following description, given with reference to theappended diagrammatic drawing, in which:

[0027]FIG. 1 is a very diagrammatic view of a vehicle viewed from above,and

[0028]FIG. 2 shows charts illustrating transmissions of LF and RFsignals.

[0029] In FIG. 1, a vehicle 2 is symbolized diagrammatically as viewedfrom above. A first rectangle 4 symbolizes the outside contour of thevehicle, while a second rectangle 6 symbolizes the cabin of this vehicle2.

[0030] The vehicle 2 represented is equipped with a hands-free accesssystem. For access to the vehicle 2, this system enables a user to lockand unlock the doors without having to use a conventional mechanicalkey. The user simply carries a tag (not represented) which takes theform for example of an electronic card. The detection of this tag andits identification authorize locking and unlocking when the userrequests same and when he carries the tag on him. Such a system isalready known to the person skilled in the art.

[0031] In a known manner, the vehicle 2 is equipped with a first groupof antennas, subsequently referred to as the inside antennas, which iscapable of transmitting an electromagnetic signal inside the cabin 6. Asecond group of antennas, subsequently referred to as the outsideantennas, transmits an electromagnetic signal of the same type as thattransmitted by the inside antennas but outside the vehicle 2. Theelectromagnetic signal transmitted by these antennas is a signal of LF(low frequency) type which, in the embodiment described, exhibits afrequency of 125 kHz. In FIG. 1, the substantially rectangular dashedcurve bearing the reference 8 symbolizes the range of the insideantennas, that is to say the zone in which the signal transmitted by theinside antennas can be picked up by a tag of the hands-free system.Likewise, two curves of substantially elliptical shape bearing thereference 10 symbolize the range of the outside antennas.

[0032] As is generally the case in vehicles equipped with a hands-freesystem, an overlap zone 12 exists. If a tag is in this overlap zone 12,it can at one and the same time pick up a signal transmitted by anoutside antenna and a signal transmitted by an inside antenna. Problemsthen arise when it is necessary to locate a tag and when the latter isin an overlap zone 12. In prior art solutions, the range of the insideantennas is considered not to spill over out of the cabin 6 of thevehicle. Hence, if a tag is detected following the transmission of alocating enquiry by an inside antenna, this tag will be regarded asbeing inside the vehicle, even if it also responds to a request from anoutside antenna.

[0033] The problem which then arises is when the response transmitted bythe tag following a request from the inside antennas does not reach themanagement device of the hands-free system of the vehicle. This canhappen for any reason whatsoever, such as for example a nuisanceneighboring transmission. So, if the response following the request fromthe outside antennas reaches the management device of the hands-freesystem of the vehicle, the tag is identified as being outside thevehicle although it is in fact inside the latter.

[0034] The solution proposed by the invention is illustrated withreference to FIG. 2. In this figure, three charts symbolize signalstransmitted. In the first chart, at the top, are diagrammaticallyrepresented LF signals transmitted by the outside antennas and theinside antennas. In the second chart, in the middle, arediagrammatically represented the responses transmitted by the tagfollowing the request from the outside and inside antennas. Finally, thethird chart, at the bottom, corresponds to the second chart with inaddition a nuisance signal. For all these charts, there is a common timeaxis along the abscissa.

[0035] In the first chart, a first gate 14 symbolizes the transmissionof an LF signal by the inside antennas. It is assumed here that a tag ofthe hands-free system is inside an overlap zone 12. This tag then picksup the LF signal transmitted by an inside antenna and corresponding tothe gate 14. It then transmits in response an RF (radio frequency)signal with a frequency of 433 MHz (another frequency of the same typemay be adopted). This response is made immediately after receipt of theLF signal transmitted by the inside antennas. It is showndiagrammatically in the drawing by a hatched gate 16. The intervalbetween the transmission of the LF signal by the inside antennas and theresponse made by the tag is of the order of a millisecond (1 ms).

[0036] After a time span sufficient to allow the tag to respond to therequest from the inside antennas has elapsed, i.e. for example afteraround 5 ms, the outside antennas transmit in their turn an LF signalshown diagrammatically in the first chart by a second gate 18. Althoughrepresented in a similar manner in the first chart of FIG. 2, the LFsignals transmitted by the inside antennas and the outside antennas maybe of different kinds, so enabling the tag to know the response expectedby the control device of the hands-free system.

[0037] The tag in question also receives the signal represented by thegate 18 transmitted by the outside antennas. It then responds to thisenquiry signal on the part of the vehicle by an RF type signal showndiagrammatically in the second chart by second gate 20. This signalcontains both the response to the request to the outside antennas andthe response that has already been made following the request from theinside antennas. This response made following the request by the insideantennas has been stored in the tag and is retransmitted insuperposition with the response to the request by the outside antennas.Thus, the gate 20 in FIG. 2 is hatched as is the gate 16 butadditionally comprises small circles corresponding to the response madefollowing the request by the outside antennas. The response thusformulated by the tag signifies not only that the tag has actuallyreceived the enquiry signal transmitted by the outside antennas forlocating purpose but it also indicates that a short time earlier it hadalready received a request from the inside antennas and that itresponded to this request. The management device of the hands-freesystem of the vehicle which receives this response then knows that thetag is in an overlap zone 12 and therefore deduces therefrom that thereis an overlap problem. In such a case, the management device will thenprohibit the locking of the doors of the vehicle 2.

[0038] The response made following the request by the inside antennasshould not be stored for too long so as to avoid the appearance of otherproblems. If the numerical examples given earlier are considered, it canfor example be assumed that the response is stored for around 10 ms.However, when the tag's search is performed outside not through asimultaneous enquiry of all the outside antennas but through successiveenquiries of subgroups of antennas, this storage time may be raised forexample to 200 ms.

[0039] The third chart of FIG. 2 illustrates the case where the responsemade by the tag following the request by the inside antennas does notreach the device for managing the outside antennas on account of thepresence of glitches. This third chart therefore also includes the gates16 and 20 which correspond to the responses made by the tag followingthe requests made by the inside antennas and then the outside antennas.Relative to the second chart, a glitch frame 22 has also beenrepresented, which overlaps the gate 16, that is to say the responsemade by the tag following the request by the inside antennas. Themanagement device of the hands-free system of the vehicle then receivesonly the response signal corresponding to the second gate 20. Since thissignal contains both a response to the request from the outside antennasand the response to the request from the inside antennas, the managementdevice knows that the tag is in an overlap zone even though it receivedno response from the tag after the enquiry signal transmitted by theinside antennas.

[0040] The process for locating a hands-free system tag describedhereinabove makes it possible to increase the reliability of thesesystems by avoiding a false interpretation by the management device ofthe signals received (and not received). More reliable locating can beachieved without requiring the implementation of hardware meansdifferent from those implemented in contemporary hands-free systems. Thesame transmitter and receiver means as those known to the person skilledin the art in respect of contemporary hands-free systems are found herealso. The electronics of contemporary tags is sufficiently developed toallow problem-free storage of a signal so as to retransmit itsubsequently. This process therefore makes it possible, withoutincreasing the price of the hardware implemented, to increase thereliability of the hands-free system.

[0041] The present invention is not limited to the process describedhereinabove by way of nonlimiting example. It also relates to anyalternative embodiment within the scope of the person skilled in the artwithin the framework of the claims hereinbelow.

[0042] Thus, for example, the signal transmitted by the tag, when it hasalready responded to a request by a group of antennas a short timeearlier, is not necessarily the superposition of two response signals.Provision may for example be made simply for a one-bit coded cue thatindicates whether or not a response following a location enquiry hasbeen made by the tag within a predetermined time span preceding theresponse transmitted. Without then storing the first responsetransmitted, the tag then stores only the fact that it has alreadyresponded to a request previously.

[0043] The frequencies, the durations, in a general manner all thenumerical values, given in the description are given purely by way ofindication. Other values may be adopted without however departing fromthe framework of the present invention.

1. A process for locating a tag for a hands-free system of a motorvehicle comprising the following steps: transmission in the form of anenquiry (14) of a signal by a first group of antennas of the vehicle tothe tag, possible response (16) of the tag to this first enquiry,transmission in the form of an enquiry of a signal (18) by a secondgroup of antennas of the vehicle to the tag, possible response (20) ofthe tag to this second enquiry, characterized in that in case ofresponse (16) of the tag to the first enquiry (14), the tag stores for apredetermined time span the fact that it has responded to a signaltransmitted by an antenna of the first group of antennas and in that thepossible response (20) made to the second enquiry (18) includes, as thecase may be, a cue indicating that a response has already beentransmitted following an enquiry originating from the first group ofantennas, the tag then being located in the zone covered by the firstgroup of antennas if a response is obtained following the first enquiry,in the zone covered by the second group of antennas if a response isobtained following the second enquiry and in the overlap zone covered bythe two groups of antennas if the response to the second enquiryfurthermore contains a complementary indication indicating that the taghas already responded earlier.
 2. The process as claimed in claim 1,characterized in that the first group of antennas comprises antennastransmitting an electromagnetic signal with a range limitedsubstantially to the inside of the vehicle.
 3. The process as claimed inone of claims 1 or 2, characterized in that the second group of antennascomprises antennas transmitting an electromagnetic signal with a rangelimited essentially to the outside of the vehicle.
 4. A process forlocating, for a hands-free system of a motor vehicle, a tag situatedoutside the vehicle, the vehicle being equipped with inside antennastransmitting an electromagnetic signal inside the cabin (6) of thevehicle and outside antennas transmitting an electromagnetic signalessentially outside the cabin (6) with a possible spillover inside thecabin (6), this process comprising the following steps: transmission inthe form of an enquiry (14) of a signal by the inside antennas of thevehicle to the tag, possible response (16) of the tag to this firstenquiry, transmission in the form of an enquiry of a signal (18) by theoutside antennas of the vehicle to the tag, response (20) of the tag tothis second enquiry, characterized in that in case of response (16) ofthe tag to the first enquiry (14), the tag stores for a predeterminedtime span the fact that it has responded to a signal transmitted by aninside antenna and in that the response (20) made to the second enquiryincludes, as the case may be, a cue indicating that a response hasalready been transmitted following an enquiry originating from theinside antennas, the tag then being located outside the vehicle when aresponse is received following the second enquiry and this responsecomprises no particular indication.
 5. The process as claimed in one ofclaims 1 to 4, characterized in that the signals transmitted by the twogroups of antennas are low-frequency signals of the order of 125 kHz. 6.The process as claimed in one of claims 1 to 5, characterized in thatthe response of the tag is made in a radio frequency of the order of 433MHz.
 7. The process as claimed in one of claims 1 to 6, characterized inthat the enquiry (18) performed by the second group of antennas iscarried out long enough after the enquiry (14) performed by the firstgroup of antennas to allow the tag time to respond to an enquiry beforeit receives another one.
 8. The process as claimed in one of claims 1 to7, characterized in that the antennas of one and the same group ofantennas transmit one after another an enquiry (14, 18) to the tag so asto limit the power of the signal transmitted.